Some vehicle display devices are equipped with a display such as a liquid crystal display, and display an image indicating information such as a vehicle speed on the display. For example, PTL 1 discloses a vehicle display device equipped with a microcomputer (main microcomputer) in charge of overall control of the vehicle display device, and a liquid crystal display including a TFT that displays an image thereon and a GDC (sub microcomputer) that causes the TFT to display the image.
In the vehicle display device as disclosed in PTL 1, communication is executed between a main microcomputer and the sub microcomputer, and a sub microcomputer generates an image on the basis of data received from the main microcomputer, and causes the TFT to display the image. In the vehicle display device as disclosed in PTL 1, it is assumed that the main microcomputer transmits data representing the vehicle speed for every predetermined time (for example, 10 msec) to the sub microcomputer, and the sub microcomputer reads out data stored in a reception buffer of the sub microcomputer for every predetermined time (for example, 10 msec) and generates an image on the basis of the data.
Meanwhile, the present inventors have recognized that a main microcomputer executes a transmission process on the basis of an own timer counter for every predetermined time, and a sub microcomputer executes a read-out process (reception process) on the basis of an own timer counter for every predetermined time. Accordingly, the present inventors have recognized that a dedicated signal line is added between the main microcomputer and the sub microcomputer to synchronize the timer counter of the main microcomputer and the timer counter of the sub microcomputer, so that the responsiveness of communication between the main microcomputer and the sub microcomputer can be improved. However, the present inventors have recognized that the cost is increased when a dedicated signal line is added between the main microcomputer and the sub microcomputer.